1. Field of the Invention
The present invention relates to an agitator drive system for use in an automatic washer including an alternately reversing drive motor.
2. Description of the Prior Art
In U.S. Pat. No. 4,542,633, an agitating type washing machine is disclosed having an agitating wheel connected by a pulley arrangement to a reversible drive motor. The agitating wheel is shown as having short, thick blades. A rotational angle detector is connected to a control that causes the motor, which is described as having high rigidity, to rotate the agitating wheel about a predetermined angle. Upon reaching the predetermined angle, the motor is deenergized until the agitator wheel has stopped, at which time the motor is operated in a reverse direction to again rotate the agitator wheel about the predetermined angle.
An automatic washer manufactured by an assignee of U.S. Pat. No. 4,542,633, and appearing to incorporate the teachings of that patent, has been observed to have an agitator stroke angle of approximately 360.degree. for each stroke at a rate of 70 strokes per minute. The high rigidity motor causes a nearly constant agitator speed in each rotational direction following a brief, rapid acceleration, and followed by the coasting to stop action.
Thus, automatic washer drive systems having reversing motors for producing a generally square wave agitation curve are known. An agitation curve is defined herein as the rotational speed of the agitator over time. A square wave agitation curve is, thus, a constant speed in one direction followed by a constant speed in the opposite rotational direction. Conversely, a sinusoidal agitation curve would result from a gradual acceleration followed immediately by a gradual deceleration of the agitator in each rotational direction.
In U.S. Pat. No. 3,315,500 to Brundage et al., a mechanism is provided as a drive system for an agitator using a motor operating at a constant speed in one direction to drive a hydraulic transmission which provides very rapid reversal of the agitator through a reversing valve and, thus, square wave type agitation motion. An elastic coupling is used between the agitator and the agitator drive shaft to reduce the shock which would otherwise be delivered to the agitator at each reversal. The patent teaches that square wave type agitation motion is preferred because more energy is imparted to the wash load.
An automatic washer having an axial air gap induction motor is disclosed in U.S. Pat. No. 4,232,536. The motor is repeatedly reversed to oscillate a vertical axis agitator through a planetary drive coupled therebetween, the motor being operated at high speeds. The desirability of providing a soft starting action of the agitator each time it reverses is recognized, the soft starting action being provided by the backlash associated with the planetary drive mechanism. No mention is made of the resultant agitator action.
U.S. Pat. No. 4,555,919 discloses a flexible vane agitator for use in a high stroke rate washer. The agitator exhibits a high degree of coupling to a wash load.
It has been found that sinusoidal agitator motion in a washing machine produces improved washing characteristics, with reduced fabric damage, and/or stretching of knits and other delicate items. However, such agitator motion has heretofore been available only by using a relatively large, complex and expensive reversing transmission between a unidirectional motor and an agitator.